1. Field of the Invention
This invention relates to a manual method and apparatus for applying a flexible adhesive strip around the perimeter edge of a rigid substrate. More particularly, the present invention relates to an improved manual method and apparatus for applying an insulating edge strip onto glass sheets as part of the manufacturing process of insulating glass units.
2. Description of the Prior Art
Insulating glass units can be manufactured using a horizontal or vertical production line.
The advantages of vertical unit production include: higher productivity; lower equipment costs; less floor space; convenient glass handling, including; large glass sheets, easy on-line gas filling, and simpler automation of various unit production operations, including, glass feed, glass movement, unit assembly and sealant gunning.
To simplify the production of insulating glass units, various adhesive strip products have been developed. One such product is described in U.S. Pat. No. 4,831,799. The product is manufactured from flexible thermoset rubber foam that incorporates desiccant fill material and features a vapor barrier backing film and acrylic side adhesive. The side adhesive is protected by a flexible release liner that allows the material to be packaged on reels. This adhesive strip product has been commercialized by Edgetech IG Inc and is marketed under the registered trademark of Super Spacer.RTM..
Adhesive strip products are typically applied with the glass in a horizontal position. As described in U.S. Pat. No. 5,246,331 issued to Hallahan et al, an air flotation assembly table is typically used. To reduce worker movement to a minimum, the air flotation table features a moveable suction cup that successively rotates the glass through 90.degree. and linearly moves the glass to a convenient position close to the perimeter edge of the table. Although the glass is located close to the operator, the hand tool must be held in position as the glass is rotated around. As a result, there can be abnormal movement of the operator's body including: prolonged spinal curvature; unnatural trunk rotation, and hyperextension of the shoulder, elbow and arm. In the long term, this abnormal movement may potentially cause repetitive stress disorders and related health problems.
For manual application of adhesive strip products on a vertical production line, the glass sheets are tilted down to a horizontal position for strip application and the strip is applied using conventional rotating tables and hand tools. For unit assembly, the glass sheets must then be tilted back into a vertical position and because of this extra glass movement, productivity is reduced.
The adhesive strip product described in U.S. Pat. No. 4,831,799 incorporates a vapour barrier backing. To provide corner continuity of the vapour barrier, a half circular notch is made in the spacer and this creates a flex point that allows for easy corner formation. Various application tools have been developed for forming these notched corners and as documented in photographs of a prototype Edgetech application tool, one way of forming these corner notches is through the use of a slidable circular punch. When activated, the hollow punch removes a half circular portion or slug of strip material. Because of the acrylic side adhesive, these slugs adhere together and as a result, the slug material can be easily ejected from the tool. The advantage is that the tool can remain in continuous contact with the glass and the productivity of strip application is improved.
At the final corner, there are further productivity advantages if the tool can also incorporate a blade for cutting through the adhesive strip. As described in U.S. Pat. No. 5,472,558 issued to Lafond, one approach is add a separate blade that operates in combination with the punch to both notch and cut through the adhesive strip at the final corner.
Although productivity is improved, experience has shown that this simultaneous operation of the punch and cutting blade requires a complicated punch design that is expensive to manufacture and is prone to wear and damage.
Compared to the earlier Edgetech tools, another new feature of the Lafond tool is that both the pneumatic cylinder and strip feeding channel are steeply inclined at angle and this has the advantage of a reduced channel length between the pneumatic cylinder and the pressure wheel. However, the drawback is that after strip cut-off, the tool requires to be rethreaded and this can be a time consuming operation.
For operating the pneumatic cylinder, the Lafond tool also features a finger trigger that is located below a cylindrical handle and operated by means of a finger pulling action. With horizontal strip application using a rotary table, there are three main ergonomic drawbacks to this arrangement. First, it provides for wrist deviation with rapid finger movement. Second, it combines forceful gripping with a twisting action and third, it requires rapid and forceful pronation with strong elbow and wrist flexion.
The tool of U.S. Pat. No. 5,472,558 Lafond is also limited to producing a notched corner. An alternative corner application detail is to partially cut through the back face of the adhesive strip and create an open-ended corner. Although in this arrangement the barrier film is not continuous, the open-ended corner allows for additional sealant material to be applied at the corners and this ensures that the edge-seal integrity of the insulating glass unit is not downgraded.